1. Field of the Invention
This invention relates generally to wind shear detection systems, and more particularly to airborne wind shear detection systems for alerting the pilot of a wind shear condition if the aircraft penetrates a wind shear condition of sufficient force to pose a hazard to the aircraft.
2. Description of the Prior Art
Various wind shear detection systems are known. Among these include ground based systems such as systems that utilize a plurality of wind speed and direction measuring stations placed about an airport in conjunction with a system for analyzing the magnitude and direction of the wind at the various stations to provide an indication of a wind shear condition. Other ground based systems utilize Doppler radar located at airports.
Airborne systems are also known. Among such systems are systems that compare airmass derived parameters such as airspeed with ground speed derived from a radar system. In the event of a rapid change in airspeed relative to ground speed, a wind shear condition is indicated. Other systems compare airmass derived signals with inertially derived signals to generate a signal representative of wind shear when the rate of change of inertially derived parameters varies from the rate of change of airmass derived parameters by a predetermined amount. Two such systems are disclosed in U.S. Pat. Nos. 4,012,713 and 4,079,905. Both of these patents disclose systems that compare a longitudinal accelerometer signal that has been corrected for the effect of gravity with an airspeed rate signal and provide a wind shear signal when the difference between the accelerometer derived acceleration signals and the airmass derived rate signals exceeds a predetermined amount. The '905 patent also takes into account a downdraft drift angle that is a function of vertical acceleration and air-speed rate. Still other systems monitor the rate of change of deviation from a glide slope beam or an ILS beam to provide a signal representative of wind shear. The system disclosed in the above-mentioned copending application Ser. No. 06/829,731, now U.S. Pat. No. 4,725,811, compares a rate of change of airspeed signal with a composite signal derived from inertially derived and airmass derived signals and does not require the inertial gravity correction utilized by the systems contemplated by the '713 and '905 patents.
While all of these systems provide some indication of wind shear, the ground based systems are responsive only to conditions in the vicinity where the transducers are placed, and are not responsive to dangerous types of wind shear such as microbursts which form and dissipate rapidly.
While airborne wind shear protection systems are more responsive to conditions in the vicinity of the aircraft than are ground based systems, many of them require Doppler radar or signals such as inertial navigation signals, glide slope signals and other signals that are not available on older aircraft. Also, the airspeed rate signals utilized by the airborne systems tend to be noisy because they are obtained by differentiating an airspeed signal. The nature of the differentiation process is to emphasize rapid changes in the signal applied to the differentiator. Consequently, short term components of the airspeed signal that are not related to wind shear produce large peaks in the airspeed rate signal. Such peaks must be limited, filtered or otherwise processed to avoid nuisance warnings. In addition, the prior art systems calculate wind shear along the longitudinal and normal axes of the aircraft or along the horizontal and vertical coordinates of the earth. This can result in errors during high bank angle turns and other dynamic maneuvers.